Hi impala community:
I having been using impala in our env. Here is our cluster deployment:
20+ impalad backend.
4 of all impalads act as coordinator.
one catalogd and one statestored
I encounter one problem that one impalad's metadata is out of sync after
catalogd restart.I find that while catalogd restarting, a DML operation is
executing.
After I analyze impala source code, I reappear the problem. this is my
steps and analysis:
1. Start the impala cluster.
2. The cluster run a long time, lots of metadata operations, and current
catalogVersion_ is big(such as bigger than 10000)
3. Submit a DML query(such as 'insert into xx partition() select xxx') to
one impalad, and the query run about 1m.
4. While the query running, I stop catalogd, and I start catalogd just
before the query execute QueryExecState->UpdateCatalog().
5. UpdateCatalog() will request catalogd for UpdateCatalog and catalogd
will update the metadata of the table and response the newest metadata of
the table.
6. After catalogd response, UpdateCatalog() update metadata cached in
impalad(call updateCatalogCache()), and the run the following code:
if (!catalogServiceId_.equals(req.getCatalog_service_id())) {
boolean firstRun =
catalogServiceId_.equals(INITIAL_CATALOG_SERVICE_ID);
catalogServiceId_ = req.getCatalog_service_id();
if (!firstRun) {
// Throw an exception which will trigger a full topic update
request.
throw new CatalogException("Detected catalog service ID change.
Aborting " +
"updateCatalog()");
}
}
serviceId is the new started catalogd's serviceId and do not equals to the
impalad's catalogServiceId_, so the function throw CatalogException and the
query get EXCEPTION, what is more, the impalad's catalogServiceId_ is set
to the new one.
7. After catalogd start successfully, and publish all metadata to
statestored, then push to the impalad, After step 6, impalad's
catalogServiceId_ equals to the catalogd's serviceId, no exception throws.
8. In normal steps, step 7 will throw the CatalogException and set the
from_version to 0 and statestored send full metadatas to impalad in next
UpdateState().
9. After all steps finish, the impalad is out of sync, all new metadata
operation will be lost because CatalogObjectCache.add() need 'new item will
only be added if it has a larger catalog version'.
Please help to confirm whether it is correct. If not, Is there any other
possibility of the problem? If so, maybe it is a bug or do you have some
suggestions to avoiding the problem.
Thanks a lot.
